Q81

Duergar Trooper has a polymorph ability that increases his size to Large. Dwarf PC that can reduce his forced movement by one square is adjacent at the time. Is the dwarf forced to move 1 square as the Duergar enlarges? Or does this allow/force the Duergar to move away from the Dwarf by a square as he enlarges? And what if there are no other locations for the Large creature to appear, what takes precedent?

Thanks!